Elk Herd Stalked by UFO

I am a UFO buff and enjoy following reports of sightings. Disappointingly, most fall short of the plausibility mark. But I'm keeping my eyes peeled.

In Colorado, men saw a UFO which they say frightened some elk:

Both Mauro and Pscholka said the object flew toward a meadow filled with elk, scared the animals and then floated out of sight. The whole episode lasted between five and 10 minutes.

I am intrigued by the observation of the scared elk. They don't say the elk stampeded away from the scene or began spinning in circles, fainting or yelling their snouts off - so how do they know they were scared exactly? Was it sort of a look?